Signaling system



Feb. 12 1924. 1,483,172

D. K. GANNETT SIGNAL-ING SYSTEM Filed April 19, 1920 z sheets-'sheet 1 W ATTORNEY Feb. 12 1924.

D. K. GANNETT SIGNALING SYSTEM Filed April i9, 1920 2 Sheets-Sheet 2 ATTORNEY Patented Feb. 12,1924.

UNITED 4s'raiilzs PATENT OFFICE..

DANFORTH K. (zrAlNlll'ETT,v OF ARYERNE, NEW YORK, ASSIGNOR T0 AMERICAN TELE- PHONE ANDTELEGRAPH COMPANY. A CORPORATION F NEW YORK.

SIGNALING SYSTEM.

` Application filed April 1 9, 1920. Serial No.l 375,077.

To all fwzofm; t'may concern.'

Be it known that I, DANroR'rH K.'GAN` NETT, residing at Ar'verne, Far Rockaway, in the county of Queens and State of New 5 York, have invented certain Improvements in Signaling Systems, of which'the following is a specification.

This invention relates to signaling systems, and especially to\means for eliminating the interference effects upon signaling currents by currents induced in submarine cables by extraneous causes.

In the operation of submarine cables, the received signaling waves are frequently disl'torted by potentials induced/in the cables by various causes, usually extraneous to thel cables themselves. Such interfering currents, upon their arrival at the receivingY station, may be of sufficient magnitude as to modify' the shape of the signaling'wave so as to render difficult the decipherm of the transmitted signal. Means have een proposed heretofore to eliminatethe effects of such interfering currents upon the transmitted signaling currents, which means em brace the use of resonant circuitsl operated as filters to transmit therethrough the signaling frequency and to attenuate,l and thereby exclude, the interfering frequency.

It is the object of the present invention to eliminate interference by utilizing the transmitting properties of devices which have a saturation characteristic such that the amplitude of the wave transmitted therethrough may be limited. By such an arrangement an interfering impulse which is characterized by a steeper wave front than the signaling impulses, will be reduced in amplitude, and consequently its resultant effect u on the signaling wave will be greatlyv iminished.

This invention will be better understood frorii the following description when readl in connection with the attached drawing, of

interference eliminating arrangement; Figure 2 shows a similar arrangement embodying a plurality of elements; and Figure 3 show-s graphically the manner in which the arrangements in Figures l and 2 perform their operations.

In Figure l, L1 represents a transmission circuit. such as a submarine cable which is adapted to have impressed thereon at its opwhich Figure l shows a simple form of the.

. i A lpo'site end, a signaling impulse for transnnsslon thereover, and 1s also exposed to 1nterference from extraneous causes. The

rcircuit L1 is connected lwith the input side is designed to rfunction as a power-limiting device. Connected with the grid circuit of the device A, are the resistance R2, the batteries B1 and Bzand the contact '9,r by means of which the grid potential ma be adjusted so as to operate at the center o the characteristic curve.between the grid voltage and the late current of the vacuum tube device. 3 is a filament heating battery and B, serves to maintain .the potential of the plate positive with respect to the filament. 'A condenser-C1 is inserted in thcl output circuit of the device A, in order to prevent the battery B4 from affecting the potential of the grid of the subsequent amplier A3. R3, R4 and are resistances of relatively large magnitudes, the resistance R3 being, for example, of approximately -one-fourth of a megohn and R, and R5 of two megohms cach. Bridged across the circuit is a condenser C., of large capacity, that is, of about four microfarads, which opel'- ates to integrate any wave impressed across its terminals so that the resultant wave is substantially the integral of the impressed wave. The integrated wavcis amplifiedby the amplifier A and passes over the,line L, to the recording apparatus.

Figure 2 is similar to Figure 1, except that a greater number of differentiating and integrating units have been provided and unilateral devices, such as vacuum tube amplifiers, have been inserted between the adjacent networks in order to prevent undesirable react-ion between the respective ele-- ments. Thus in Figure 2, the amplified wave yis impressed across a circuit embracing three differentiating networks in series, which networks are represented by the resistances and transformers R1 and T R and T2,and R, and T3, respectively. The adjacent/networks are separated by the vacuum tube devices A4 and A5. vThe power-limiting device A2 and its immediate circuits are similar to those shown in Figure 1, and need no further description. The l@ output side of the device A2 comprises the same number of integrating networks as there were differentiating networks in the input side. Thus the resistances and condensers, R5 and C2, Rs and 0 and R, and l@ G represent integrating networks .which are separated by the unilateral devices A f and A7. The output sideof the last network is connected with the amplier A3 which in turn is connected with the'line L2, 2@ with which the receivingapparatus is connected'. f Y

Fi ure 3 shows graphically the manner in whicthe arrangement shown in the previousligures eect the desired result. ln this 'gure, a-represents a signaling Wave such as may be transmitted" over a submarine cabie in which an impulse in one direction represents a dot and in the other direction a dash. The curve a represents the Word sat comprising vthree dots, a dot and dash, `and. a dash.V The curve bvrepresents the eifect'upon the signaling wave of impulses set up within the cable by causes usually foreign to the cable itself. Such impulses are usually in the nature of a transient having a steep wave front and which is ,generally quickl damped. The curve c represents-Vthe orm of the Wave b after it has passed through a` differenti-ating network. The wave o is impressed across the grid circuit of the power-limiting device which has a characteristic curve represented by f. it will be noticed that the curve f is symmetrical with respect to the y axis which e'ect 'is obtained by the proper adjustment of the contact 9 along the resistance R2 in the grid circuit of the device A2 in Figures 1 and 2. The curve d represen-ts the output current of the device A2. This device is so operated that the dierence between the values of grid voltage corresponding to the saturation limits of the device is substantially equal to'I the difference between the upper and lowerlimits of that part of the curve c, produced by the signaling wavel and not by the interfering wave. lVith thedevice A2 so adjusted, the signaling Wave will be transmitted therethrough without diminut'on in amplitude, .but the peaks of the curve c, which represent the differentiation of the interferin component of the wave will be eliminate which means a reduction in the amount of sents the output of the integrating network interfering energy.- The 4vcurve e repre i maarre which shows the manner in which the si naling wave has been restored to .approx-iheld' vertically) corresponds in pointi of' time to the left-hand end of the curve d. Thus, the fluctuations of curved from left to right corresponds with the fluctuations mately its-original form, and the interfer@ of the curve c:A upward in the direction of the arrow X.

Having in mind the foregoing. description of the various parts which are represented in the diderent figures and ofthe functions or purposes of each of the parts, this invention 'will be more clearly understood from the following description of its mede of operation. 2

if there be transmitted 'over the line L,- as'shown in Figure l, a Iwave' such as is shown by b in Figure 3, the am litude of the im ressed wave will be ampli edfbythe ampli er A, to such an extenttli't'the distance between the maximum positive and negative values will'be substantially equal to the grid potential corresponding to the distance between the vam's and the upper saturation limit of the characteristic 'curve of the device A2. The amplified Wave is` then impressed across the primary winding of the transformer T, which inducesl in the secondary winding 2 a curve which is substantially the form represented by c in Figure 3. This curve a will produce variations in the grid-potentialcorresponding to variations of the impressed wave and there will result in consequence variations in the plate current Within the limits represented by the distance between the axis and the upper saturation limit of the characteristie curve. ln view of the nature f a device which has a saturation point in its operatlng characteristic, the outputv wave form corresponds to the input wave form onl within the saturation limits. Since the device will not pass current proportional to the peak values of the curve C, much of the energy represented bythe interfering impulses will e eliminated by the powerlimiting device A2. issues from the output of the device A2, is impressed across the network represented by the resistance R5 and the capacity C2, the form of the WaveI will be changed thereby, and the resulting wave e will be the integral of the impressed wave d. The wave'e, which is substantially the signal wave a, most of the effects of the interfer- If the wave d, which v Het) Ling impulses beingeliminated, `will ,be iln pressed across. the amplifier A3 and the amplified resultant wave will in turn be impressed across the line L2 with which the recording apparatus is connected. v

From the foregoing, it will be seen that 1f a signalwave which is-distorted by interferinterfering. wave -is substantially the same as that of the signaling wave, that is to say, that the rate of change of the current is substantially the same. -Since the voltage acrss the inductance is proportional to the rate of change of the current, if the rate of c change of the two impressed curves be substantially the same, there will not be suffi- `cient difference between the maximum values of the differentiated. wave to enable the current-limiting.device A2 to properly v eliminate the effect produced by the interfering wave. Since, however, the frequency of the interfering wave impulse is usually greater than that of the signaling'impulse, we may effect the desired separation by differentiating the impressed wave several times, which tends to increase the amplitude of the interfering wave more than the other wave, Such an arrangement is shown .in Figure 2, and by integrating the wave the same number of times as it was differentiated, we may obtain the signaling wave freed substantially from the effects of the interference. K

Although this invention has been disclosed in a certain form, it is capable of embodiment in other and di iferent forms wi thout departing from the scope of the appended claims.`

lVha-t is claimed is:

1. In a signaling systein the combination with a signal transmission line exposed to interference from extraneous sources of a network comprising bridged inductance across which the waves transmitted over the said line are impressed and adapted to produce the first derivative of the said waves, a translating device whose characteristic curve has a saturation point upon which the said derivative wave may be impressed whereby the amplitude of the wave may be limited and a second network comprising bridged capacity across which the output wave of the said translating device may be impressed whereby the integral of the impressed wave may be'obtaine A 2. In a signaling system, exposed to interference from extraneous sources, the combination with aFV signal transmission line exposed to interference vfrom extraneous sources of a plurality of networks comprsing bridged inductance, the respective networks being separated from each other byIl unilateral devices, a translating device designed to limit the amplitude of the wave transmitted therethrough and a plurality of networks comprising bridged capacit-y separated from each other by unilateral devices whereby the interference component ofthe signaling waves may be substantially elim-- inated. .f

3. In a signaling system, the combination with signal transmission means exposed to interference from extraneous sources of a network designed to effect electrically the differential of the vwave impressed thereon, a translating device havin a saturation characteristic, the upper andIower limits being symmetrically related to the Y axis which may be operated so as to cut off all values of the impressed differential waves above the maximum value of the differentiated signaling component and a second network connected with the output side of the said translating device designed to effect theintegra.` tion of the wave impressed thereon whereby the effects of extraneous interference uponthe signaling waves may be minimized.

4. In a signaling system, the method for substantially eliminating the effect on signaling waves of interference from extranecharacteristic curve has a saturation point I upon which the said derivative wave maybe impressed .whereby the amplitude of the wave may be limited, and a second network 1 across which the output wave of the said translating device may be impressed whereby .the integral of the said derivative wave may be obtained.

6. In a signaling system, the combination with a. signal transmission circuit exposed'to interference from extraneous sources' of a network across which the waves transmitted over the said circuit are impressed, and adapted to produce the nth derivative of the said waves. a translating device whose characteristic curve has a satura-tion point .upon which the said derivative wave lmay be 1mpressed, whereby the amplitude of the wave may be limited, and a Second network across which the output wave of the said translating device may he impressed whereby the nth integral oi' the derlvative wave may be obtained. y Y

7. In n signaling system. the method for substantially elimina-ting the effect on signaling` waves of interference from extraneous sources, which consists in the successive differentiation toA the nth degree of the distorted wave, limiting the magnitude of the mesma differentiated wave to a predetermined mex` 10 imum value, and successively integrating -to the nth degree the said differentiated wave as thus limited. y

In testimony whereof I have signed my name to this specification this 16th day of 15 April 1920.- l.

' vDMQFORTH K. GANNETT. 

